Influence of waves and currents on the growth rate of the kelp Laminaria digitata (Phaeophyceae).

The kelp Laminaria digitata growing in the low intertidal region along energetic coastlines are exposed to a range of hydrodynamic environments. Macroalgae in the intertidal zone can experience both waves and currents independently, but it is unknown how they influence growth rate. Relative growth rate of the meristematic region and the entire blade of L. digitata were measured to assess the influence of wave and current motion from three hydrodynamic environments: low current and low wave (LCLW), high current and low wave (HCLW), and high wave and low current (HWLC). Alongside hydrodynamic data, seawater nutrient concentrations and temperature were also collected and analyzed. Results suggest that differences in L. digitata relative growth rates were not attributed to the seawater nutrient concentrations or temperature, but attributed to the hydrodynamic environments. At the high current condition, kelp growth rate of the meristematic region was enhanced by 45% compared to the high wave condition. When including the entire blade growth rate, an average increase of 25% was observed between the high current and high wave condition. Potentially, the division in growth rate observed between the wave and current motion is related to the frequency and magnitude at which the hydrodynamic forces act. These findings highlight the complexity of the hydrodynamic environment and that forces associated with waves and currents may have a significant role on the productivity of kelp.

Serendipitous re-sighting of a basking shark Cetorhinus maximus reveals inter-annual connectivity between American and European coastal hotspots.

Transatlantic stock mixing in basking sharks Cetorhinus maximus is supported by low genetic diversity in populations throughout the Atlantic Ocean. However, despite significant focus on the species' movements; >1500 individual sharks marked for recapture and >150 individuals equipped with remote tracking tags, only a single record of transatlantic movment has been previously recorded. Within this context, the seredipitous re-sighting of a female basking shark fitted with a satellite transmitter at Malin Head, Ireland 993 days later at Cape Cod, USA is noteworthy.